Tact is a skill. One needs to effectively know when to be direct and when not to. Not understanding this very much is a problem and it will in fact affect your relationships with others. Lacking tact is a part of social awkwardness; and yes, an MI does come to mind.

A very big part of learning when to be direct and when not to lies with that of effective communication skills. One must be good at reading non-verbal communication and signals. One must learn to read the situation and make their choice accordingly.

There are those times when being direct is in fact required but one needs to carefully draw upon their tactful skills. To be direct, you need to gauge your ability to be diplomatic before proceeding.