关于“a bit of life experience under his belt ”请问为什么用under his belt?是俚语吗?

关于“a bit of life experience under his belt ”请问为什么用under his belt?是俚语吗? 关于a bit,a little,a little bit,a bit of这三个词组各自的用法和区别 a bit of a bit和a bit of用法 英文His life has been a little bit of a roller couster.是啥意思? a bit of a bit a little a little bit of a lot of a lot bit of 用法 以a bit of 造句 a bit out of hand that's a bit of 用quite a bit of Not a bit of it! not a bit of it A little bit of privacy, a bit of 什么意思? a bit of the harbour a bit of everything 是什么意思? little,a bit,a little bit,a bit of与a little of的用法! a bit a bit of a little a little ofa bit a bit of a little a little of a little bit of的区别?