#4 is short. Everything and everybody is higher than he is, always. So, he wants to go up. Turn around for 30 seconds and he’s climbed something. Chair? Sure. Table? Why not? Stand on it or sit – well, the one that gets him higher. Is the chair stable? It matters not a bit to him. Tipsy barstool? He’ll climb it. Narrow bench over hard floor? Up he goes. Across the gap between couches? If he wants to cross it, he’ll try. Standing on the arm of a couch to reach the chalkboard? Of course! Did I mention he’s 18 months old and none too steady on his feet?
He mostly stopped standing up at full speed CLUNK into the bottom of the table. He even stopped stripping stuff off the sides of tables. Now, he’ll be found on a chair, reaching for the middle of the table. The boy is a climbing machine. Just like his other two brothers and their daddy and their grandpappy. It’s a boy thing. It’s no use asking “WHY!? Do you INSIST on CLIMBING EVERYTHING?@!”
That’s why they called it the “Y” chromosome, don’t you know.