There are plenty of Nazi war diaries of German troops pissing and shitting themselves when they found that their anti-tank weapons couldn’t hurt T-34s or KVs in 1941.

although not to be a downer, this is mitigated by the fact that t34s were very rare at that point (as the soviets were smack dab in the middle of rearmament). They mostly encountered the weaker BT-7’s and T-36 and T38. It took until a year or two until they were really fucked. The Soviets were the only side that truly knew how to win that war, their main tank could go at very high speeds while 1v1ing the tiger tank. Germans were fucked by 43.