Your first question is impossible to answer, frankly. It is simply an impossible task to determine whether or not men went to war because they wanted the great outdoors and thought it'd be over soon or if they were nationalists or if they were just young and dumb. That's a kind of statistic we can't reasonably create. However, we do know the statistics of men from certain industries that would volunteer for the army and it is in the low 20%'s for coal miners -- 20-22% depending on the source and year. This is on par with other industries like iron and steel refinement and would be less than those of the electric and engineering trades.^[1] There's no real reason to look at these numbers and say miners (particularly coal miners) would volunteer disproportionately to escape their conditions.

People were happy to sign up for the war, yes, and they did believe it would be over quick. It was almost over quick as the Germans were on the outskirts of Paris less than 40 days into the war. However, by 1915 and 1916 and onward many recognized it would not be over soon but would still find motivation to join. Mainly through a combination of public shaming of those who refused to go serve and through a historical tradition which glorified war as an adventure and something "men" do. Beyond the British, the French would sign up to defend their homeland and the Germans would sign up to secure German Weltmacht -- world domination / world power and we can do this same song and dance for every other nation. It's pretty situational but yes, every nations men had their motivations for volunteering. This was a different time than ours when war still was glorified and seen as a pretty good thing.

It wasn't and these perceptions would be shattered in the aftermath of the war. This is kind of where I go off on you, so pardon me! In many respects World War I was the purest concentration of every horror of war jam packed into one war and more specifically one front. We all talk about how horrible life in the trenches was and man, must've sucked to be those guys huh?! Do we really know what these men lived through? We are talking about thousands of years of cultural history in the West which glorified war and it being shattered in 4 years flat. Seriously, how traumatic would it have had to have been?

I never could stand shell--fire. I got into a thoroughly neurotic state during the day. Enduring a bombardment is the opportunity for that kind of nervous disease which made Dr. Johnson touch every post as he walked along Fleet Street. You think of absurd omens and fetishes to ward off the shell you hear coming. . .

So all the day you listened, calculated, hoped or despaired, making imaginary bargains with fate, laying odds with yourself on the chances of these various horrors. One particular gun would seem to be firing more directly on you than the others. You would wait for its turn so intently as to forget other perhaps more real dangers. At last it comes. You hold frenziedly on to the conversation; you talk a little too fast; your nerves grow tense, and while you continue to look and talk like a man, your involuntary muscles get a little out of hand. Are you knees quivering a little? Are you blinking? Is your face contorted with fear?

You wonder and cannot know. Force yourself to do something, say something, think or something, or you will lose control. Get yourself in hand with some voluntary action. Drum out a tune with your finger-tips upon your knee. Don't hurry - keep time - get it finished and you will be safe this once. Here superstition and neurasthenia step in. Like the child who will not walk on the lines in the pavement and finds real safety in putting each foot on a square stone you feel your ritual protects you. As the roar of an approaching shell rises nearer and louder you listen in inward frenzy to the shell, in outward calm to the conversation. Steady with those nervous drum-taps on your knee; don't break time or the charm is broken and the augury vain. The shell roars near. What was Thorburn saying?

"Oh yes!"[sic], the rations come up at nine o'clock, enough for twice our numbers."

This is a journal entry from one Charles Edmonds describing his experience with a single artillery shell he hears during a casual conversation and in my opinion perfectly encapsulates mood of trench conditions -- one of persistent, neurotic terror.

Many people like to bring up how men only served in front line trenches for about 7 days and would then cycle out to a rear trench to "rest" for a week or two, implying that life was cushy and more laid back than we think. They would generally not get such comfort, you did not escape the war and its horror. If you were on "rest" your job was generally to act as one of two jobs -- a runner or a supplier or in a worker party. A runner would have to run between communication trenches and the front line to deliver messages and vice versa. Since we didn't have trucks and armored vehicles of any kind all supplies would have to be delivered by hand. We're talking about food for tens of thousands of men stationed on the front line in a sector, and those on "rest" would have to do this.

As you approached the front delivering your steaks and rum and other rations it would likely be in the dead of night to shade you from snipers, which were a constant threat and you couldn't exactly be subtle lumbering around with goods. The darkness would not stop them from still popping off shots at you. The water would be knee high at least in more hot sectors and even up to the waist at times. It would not be that clear Hawaii water, it would be grungy, muddy, bloody water. You would have to negotiate these cramped, usually unfamiliar trench systems in pitch blackness all while carrying a couple dozen kilograms of rations while being under periodic sniper or machine gun fire. If you were in a "quiet" sector (ie: one of significant distance from enemy trenches) you replace "sniper" and "machine gun" with "constant artillery shells around you" and "offensive patrols."

Speaking of that, let's talk the life of a soldier on a front line trench. Your job, all day, was to fortify your trench. Refilling sandbags (which didn't use sand but clay) and packing them in defensive positions. You will note that by putting sandbags in damaged or unfortified areas you are inherently exposing yourself as you lay them down. It was very nerve wracking. You would be clearing water out of your trench, digging up bodies and burying them, dealing with the smell and defecation of all types, and hiding in tiny holes whenever artillery barrages occurred. That or hitting the deck in that aforementioned grungy, muddy, bloody water when a snipers shot snapped right above your head and you were pinned down. Or crawling out over the top to lay down barbed wire to replace damaged sections. Note how the enemy had offensive patrols specifically designed to hunt people like you down who were reinforcing barbed wire fortifications which at times extended dozens of yards or even hundreds of yards out.

Your actual combat duties would include covering worker parties, going on patrols, and going on raids. Going on patrols basically meant walking out into no mans land with a handful of buddies and trying to scout out enemy positions without getting shot by a sniper or a machine gun or an enemy patrol. Being an offensive patrol meant you went and attacked enemy worker parties...who were being covered by hundreds of men and snipers and machine guns. Being a raid meant you and 100-500 of your buddies ran across no mans land and tried to capture prisoners in the enemy trench and then run back to your trench to interrogate them. As you might imagine, this is a pretty shitty experience overall. If you somehow managed to survive all these things trying to kill you, you would spend days and nights sleeping to the sound of artillery shells weighing hundreds of pounds at times blowing up a couple dozen yards from you and constant machine gun fire and eating wet steak and potatoes and drinking cheap rum. Then you get to cycle back a couple hundred yards back and spend the next week or two navigating the trenches and delivering supplies and messages all over again and maybe, just maybe, a few days out of the year you get a few days of legitimate rest.

---

"Life and Death in the Trenches of the First World War", Andy Simpson

"Tommy: The British Soldier on the Western Front", Richard Holmes

[1] "The First World War: To Arms", Hew Strachan is the only source off the top of my head that talks about this explicitly but I know there are more.