What is trade thesis?

A useful thesis fits in two sentences: the expected move and the evidence behind it. For example: "BTC is holding its weekly support after a 30% pullback while funding has reset. I expect a move back to the prior range high, and a weekly close below support invalidates the idea."

Writing it down does two things. It forces you to separate evidence from hope, and it gives your journal something to check the result against.

Following someone else's trade without their thesis means you cannot manage it when it moves, because you never knew why it was taken.