There are two kinds of professionals. They are: 

A. My-best-effort

B. Whatever-it-takes

Let's say you are looking to party on Friday night. The boss calls you and asks you to submit some test results by Saturday noon. 

Here is how the two professionals will respond to that: 

A. My-best-effort

"Sure, no problem!" 

Then you go on and party the night away, forget all about the test results. When your manager messages you at Saturday 5 pm to check if you have uploaded the test results, you say something like, "Hey, not yet." 

You then get to it on Monday, in a business as usual mode. Apologies are for losers(Meaning, you do not apologise because there is nothing to apologise for) and if entire projects can get delayed, why cant simple test results be delayed by a bit? Whats the big deal? 

B. Whatever-it-takes 

You tell the manager - "I am sorry, I am meeting friends tonight and have plans this weekend. The earliest I can get to this is Monday afternoon. Will that be ok?" 

The manager thinks you have a bad attitude and gives it to the my best effort person. On Monday  morning, it lands at your desk (on account of Hey-Not-Yet) and you give a timeline of Tuesday afternoon to submit the test cases. 

Monday 1600 hours you realise this is going to take longer than that and you gave a wrong estimate. 

You then work to complete it, submit it by Tuesday afternoon, and never give a wrong estimate on a task like that again.