He is clever, but on the other hand he often makes careless mistakes.

He had a reputation for carelessness.

He was rather careless to say the least.

Do not answer hastily.

Don't behave lightly.

Carelessness is his principle feature.

We shall never agree on such a careless plan.

It is careless of you to say such things.

The failure is due to his carelessness.

The movie star ate crow many times because of all the thoughtless things she said.

This mistake is due to his carelessness.

They got the sack for being careless and tardy.

The actions she took were too careless, and she was left defenseless.

I spoke without thinking, sorry.

Tom should've known better than to call Mary after midnight.

I was careless.