The P38 is like a 1911 in a lot of ways - large and small in just the right places. The side profile view is probably one of the slimmest in the game, so if you're decent at pointing your wing at the enemy who is shooting at you, you present probably the most difficult target in the planeset to hit.
I will say fighting in a situation where you are overwhelmed, the P38 is certainly not the plane I personally would want to be in, you know, one of those one or two of you left after a big furball, and about 7 or 8 bad guys. Spit5/Hurricane/N1k, and even maybe some of the 109s I'm often able to fight my way out of these situations I quite often find myself in due to how I fly (stupidly from a survival viewpoint sometimes), where is in the P38 if I'm lucky I'll get one or two of them before I present a huge easy profile shot to somebody and die. For a pilot smarter than me that can stay out of those situations for the most part, it's easily the most overlooked aircraft which is able to win in so many ways. I read something somebody here wrote, that the planes the P38 can't turn or maneuver with, it can outpace, and the ones it can't outpace it can outurn - pretty much always has a strength someplace vs every other plane out there, that if you're good in it, you can exploit (again, not me).