Now while he was in Jerusalem at the Passover Festival, many people saw the signs he was performing and believed (ἐπίστευσαν) in his name.
But Jesus did not trust (ἐπίστευεν) himself unto them because he knew all men (John 2:23-24)
The same root word in Greek is used to signify both the faith professed by the people in Jerusalem who are impressed by the signs performed by Jesus, and the thing Jesus will not offer in return.
They offer some sort of faith in His name, but He has no faith in this faith, as it were.
John explains why in the next verse ...
and [Jesus] didn't need anyone to tell him about human nature. He knew what people were really like. (John 2:25)
Knowing their hearts - even without being told - Jesus knows that their faith is not such that He could entrust Himself to them. Indeed, neither could Jesus count on the faith of His closest disciples, who all abandoned Him in His hour of need.
So He keeps a wise reserve.
Jesus, you see, is not a publicity hound.
He is not like us actors who think that applause = love.
He knows man better than that.
(Here Roxie Hart explains the psychology of show business - kid. There's a bit of profanity if you watch it to the end.)