i read that poker without a plan is bad poker

but i nomally don't plan in future street.

i only think what i face

for example i don't have plan turn and river situation in the flop.

(ex. i will call the turn. but if he bet river, i will fold)

or i don't think that "i will 3bet but fold to 4 bet"

why is it important to have a plan in poker?