If you've been a shitty worker in the past, this is the time to redeem yourself. Show them that you change and and has changed permanently. Become a fast worker that never breaks promises. And also even if you are fast, make sure that your work has a very high quality. Forget about the managers that scolded you because you're caught sleeping while working. Forget about your teammates that got disgusted with you because you're such a burden to them. It is time to show them that you too can reach a certain level that will make a difference. Forget everything, forget the deadlines that you missed, the clients that got angry, the co-workers that wanted to kill you because you never made a big contribution, instead you promote repetition. Forget all of it, this is a new day, take it seriously and never look back.
If you are weak from the past, if you can't even run fast, if you can't even lift a 10 kg weights... you should redeem yourself, are you just going to allow them to call you weak? Are you just going to allow someone beat you easily? You know, it is not that you are weak, you are just afraid to try so hard. You are just afraid to push. What is it to be afraid of? If it can't kill you then don't be afraid of it. If it is going to make you strong then go for it. You have nothing to lose, you have everything to gain.
Remember that what you are doing now has nothing to do with what you did yesterday. So if you suck from the past you can make the present a blast. You can stun them, amaze them and make them feel that you are a changed human being. It is like you're Clark that transformed into Superman or Frog into a Prince.
Redeem yourself now or you can't redeem it later. The more you postpone on changing yourself, the more you become worse than yesterday.
Anyone can redeem himself for as long as he is serious about it, and when they already found out that you've changed... maintain it, never go back on being weak again. Completely transform yourself. Maintain that strength and it is much better if you can make it stronger.