The thing about Pacific Rim is that it's an allegorical fairytale.
The Jaegers are an allegory for the things we can't do alone without burning ourselves out. Yeah, it's possible to pilot a Jaeger solo for awhile. But nobody can last the whole fight. If you try, you will collapse under the strain sooner or later. You will die.
The drift is about the necessity of making yourself vulnerable to someone, letting another person in, so you can lift this otherwise impossible burden together. Because if we isolate ourselves, if we don't face the mortifying ordeal of being known, we will change nothing, and we will die alone.