I'm currently pursuing a minor in WWII history so I'm definitely not as qualified as many of the historians in this subreddit but I have taken a lot of classes pertaining to WWII. It always appeared to me that the beginning of the war was when the Germans were at their best. They seemed to beat the Allies in every confrontation because they were better equipped and more prepared. They effectively used their superior armor and firepower in their new Blitzkrieg (lightning war) tactics to quickly overrun the French, Russians (up to Stalingrad), and anyone who stood in between. They also enjoyed success in Africa early in the war due to the outstanding leadership of Rommel. It seemed like nothing could stop the Germans, and as it turns out, ironically enough, they stopped themselves. They over extended themselves in Russia. They were totally unprepared for anything less than success as they had planned it. The hadn't produced nearly enough winter clothes to sustain themselves should the war with Russia stretch to the winter. But Hitler believed that Russia would fall before then, which we know they did not. Hitler's arrogance hurt the Nazis yet again when he decided to split his army and head for Stalingrad instead of taking Moscow. The failure to take Stalingrad is often considered to be the turning point in the war; when things really began to look bleak for the Germans. The war on the Eastern front swallowed German resources as well as men. I remember reading that for every 1 German soldier killed by both British and American troops, 4 were killed on the Eastern front by the Russians. I'm sorry I'm rambling I'm writing this as I'm thinking of it. The Germans lost the war for main reasons in my mind (and again I'm not the most qualified person here) because of Hitler, and because they were German. It seems to me that the Allies were the ones who got lucky the most often in the war. Had Hitler not wanted to be personally in charge of releasing the armored divisions in Normandy or had he not had made it known that whoever woke him up before he awoke at his own pace, the panzer divisions could have been released on the unstable beachheads on DDay. This likely would have caused unimaginable destruction and could have changed the outcome of the entire operation. But that's enough about Hitler, the German's stubbornness and inability to adapt plans to changing circumstances played a large part in their defeat as well. After the Allies cracked Enigma the Germans knew that something wasn't right. They almost immediately dismissed the idea that the code had been creaked because by God it was unbreakable. So instead they thought espionage and killed a couple of their soldiers. It's also been said that the Allied troops in Europe were much more effective than the Germans because of their ability to deviate from plans and improvise in the chaotic hedgerows whereas the Germans followed orders unto death. So to answer your question; no. The Germans were not merely lucky in the beginning of the war. If anything luck was on the side of the Allies. We were lucky Hitler was as batshit crazy as he was and the Germans unwillingness and inability to stand up to him. There are plenty of other reasons for me to believe that luck was on the side of the Allies such as the Battle of Midway. It seems like that was a fluke that we should have even put up a fight let alone win decisively. But that's what makes WWII so interesting and what makes me want to learn more about it. There are so many instances when only a few moments determined the fate of the world. There were also events that took much longer to unfold. Both of which are important to learn from because of their impacts on the outcomes of major events. Well that's all I've got for now, I hope it helped answer your question. Sorry for the rambling and jumping around. Back to writing my paper!

TLDR: From what I've read/been taught the Germans enjoyed success initially because of their better weapons, tactics, etc. Then they did some dumb stuff, ended up fighting the Russians in the winter and the shit hit the fan. It seems like we were the lucky ones during the war (Battle of Midway among other things)