When we use very, it's not clear whether what we are describing is a good or a bad thing.

在我们用 “very” 时，并沒有表明所叙述的事情是好是坏。

The building is very old.

This could be a good thing: 'the building is old and beautiful'. It could also be a bad thing: 'the building is old and falling down'.

这可能是好事儿：“这幢楼历史悠久而漂亮”。也可能是错事：“这幢楼很老，就需要塌了”。

Too = 过度、太

When we use too, it means there's a problem.

在我们用 “too” 时，代表着所叙述的事儿有什么问题。

The building is too old.

This is a bad thing. The building is too old. It might fall down and could be dangerous.

这暗示着楼很 “历史悠久” 是件错事。这幢楼太老了。它很有可能会塌陷，很危险。