"Time stays long enough for those who use it."
Leonardo da Vinci
Thinking back over my career, I believe "I didn't have enough time" was the number one reason my direct reports gave me when they hadn't completed something when expected.
Sometimes they were stating fact and they didn't have enough time; however, I doubt that was true in less than 1 out of 5 cases.
The other times? They simply didn't manage themselves well enough (and yes that applies to me as well.)
How about you?