We should know what we are getting into before we commit ourselves.
look before you leap
Think of the consequences before you act, as in You'd better check out all the costs before you buy a cellular phonelook before you leap. This expression alludes to Aesop's fable about the fox who is unable to climb out of a well and persuades a goat to jump in. The fox then climbs on the goat's horns to get out, while the goat remains trapped. [c. 1350]