To "collaborate" means to work together with someone else to achieve the same goal. You collaborate on a project or a problem, etc.. When you do this you are working in "collaboration". To "alleviate" means to make something less severe. Let's pretend you are a doctor who works by himself in a little village. There are no other doctors in the village. You will have many patients who have a great variety of problems. You may have someone who has a broken foot in the morning, and you may have a pregnant woman in the afternoon. The next day you may have a person with a serious skin disease in the morning and another who is losing his vision in the afternoon. Because you are alone you would have to be "all things" for all these people. You would have to be an expert in bones, pregnancy, skin diseases and eyesight. There is no one else to help you! This is very stressful, right? But if you work in a city and in an office with many other doctors you could collaborate with them. So, one of you is an expert on pregnancy and another is an expert on eyes, etc.. Each patient is sent to the appropriate doctor and you don't have to do everything yourself. This sort of collaboration alleviates the stress of trying to be all things to all people.

"trying to be all things to all people" means trying to make everyone happy, even though different people have different desires. So it will be very hard to make everyone happy, because you will have to constantly change yourself.