If someone is apt to do something, they often do it and so it is likely that they will do it again.
likely or having a natural tendency to do sth 易于…；有…倾向
~ to be…
apt to be forgetful/careless
健忘；常常粗心大意
~ to do sth
Babies are apt to put objects into their mouths.
婴儿爱把东西往嘴里塞。