Unless you are the type that likes being in his or her comfort zone always, there must have been a time you strive to become better at a thing or achieve something, and having someone strive for that same goal sort of accelerates the speed of your drive to achieve that goal. This is what is referred to as healthy competition.
I've had to compete with a friend or colleague at several points in life, not because I want to be better than them and feel superior, but because we sort of sharpen each other through encouragement, correction, and celebrating each other's wins. On Hive for instance, I remember when my friend 
There are some set of people who go into unhealthy competition due to jealousy and resentment with the aim of putting the other down, for these set of people, it doesn't always end well because their goal isn't clear, they are just about outshining others and not really focused on self improvement, they have so much hate in them, this is how you identify toxic competitors, they can go to any length to bring their competitors down.
Unhealthy competition is also what pushes some people into debt, as they want to go out of their way to belong, and this is common among foolish wives, who often do not appreciate the effort of their spouses and always want to compare their family to that of their friends. This is one of the reasons I prefer my introverted nature, I don't seek validation or competition to feel enough, I move at my own pace when it comes to family issues
I once heard a story of how a woman almost destroyed her home because her husband would always buy fish as the only protein source for their food instead of chicken his wife wished for, all because her friends usually boast of eating chicken with every meal, but her husband provided what he could afford which wasn't always to the wife's satisfaction. It wasn't until her friend had issues in her home that it escalated to a big fight did she discovered her friend was lying all the while and her supposed husband wasn't even providing any food talkless of chicken, it was all a show to make the friend feel jealous and she fell for it.
I always remind myself no matter how tough the situation gets, that there is always room to overtake, as long as you keep giving your best at whatever you do, your pay day would surely come, life is a journey, not a destination and there is no need to get jealous of someone success, instead you should be happy for them and learn from experience, also continue putting the work and success will sure be guaranteed.
And if you have friends or partners with the same goal and no jealousy in the way, by all means, encourage each other and get better together hitting milestones.