The self-help and life-hacking industries have us fretting about optimising every single facet of our working lives, but often this is a total waste of time. There are plenty of things at work which aren't really worth worrying about. So what should you be letting go of?Giving 100% and perfectionismWhen you deliver perfection, you're focusing on what you're doing, not on the impact it has. This is the basis of the Pareto Principle, which states that 80% of the effects come from 20% of the causes.Second, we have the law of diminishing returns, which means as you get closer to 100%, you expend much more effort on the remaining work: the last 10% could take as long as the first 90%. Or you could do 100% on one job or 90% on two jobs - that 90% may be more than enough to satisfy your boss.Gossip about job movesMany people devote enormous amounts of energy to finding out about internal moves and reorganisations, but there's little point. Unless you're at the top of the heap, few of these will affect you.Taking sick daysThink about how you feel when a colleague is coughing constantly. All you ever think is, "Go home". That is how everyone else feels about you when you come in sick. They don't thank you for bravely struggling in, they want to you to leave before you infect them.Taking holidaysNo one will steal your job, nor will they discover they can cope without you. Going on holiday will mean you come back rested and more productive.Should you check your e-mail?Sure. Should you check it every two minutes? No. Researchers at the University of British Columbia found that people allowed to check their e-mail only three times a day had lower levels of stress compared to those who were allowed unlimited access to e-mail.RevengeYou work in a professional services firm, not the Mafia. When Justine got that job rather than you, she didn't stab you in the back, she applied like you did and met the criteria marginally better.Home-ing from workDo you check e-mail in the evenings? Do you have to do conference calls with American colleagues at 9pm? Do you travel for work? If the answer to any of these is yes, why do you worry so much about your manager or colleagues seeing you doing a bit of online shopping or booking a flight?MeetingsIt's human nature to worry that if we do not go to a meeting, matters of great importance will be discussed and momentous decisions taken. But contrast this with any real meeting you've been in.Nothing gets done and you spend half your time listening to that colleague who won't shut up. So only go to meetings if they're important or mandatory.People who are doing better than youSome of your colleagues will simply be more talented than you and chasing their tails will be a dispiriting waste of your time. Others will be harder working - and here, you have to ask yourself, do you want to give your life over to the company? Others will be luckier and there's not much you can do about that.Think about what your own goals are - not your colleagues'.Your boss hardly ever praises youWe'd all like to be slapped on the back and told what a great job we're doing at the end of every little task. But not every manager is like this. Instead tell yourself that when they do say "Well done" it's an amazing compliment, and if they say nothing they're happy with you.© The Daily Telegraph..