organic chemistry - Mechanism of hydroboration oxidation reaction

I know that the hydroboration reaction is used to add $\ce{H2O}$ to the double bond in an anti-Markovnikov fashion.

I went to the Wikipedia page and found the following mechanism:

But I could not understand as to why the addition is syn.

Answer

The addition is concerted, i.e., everything happens at the same time; there aren't multiple steps to the addition. You can expect the boron to go on one face of the double bond while the hydrogen goes on the other face. There's just no way for the hydrogen to reach over to the other side for the anti-attack. It has to be syn.