To strive or not to strive

So the question thats been on and off on my mind is "Should an individual strive too hard to achieve success or should he start enjoying life and take things as it comes?"

Two extreme scenarios that come to my mind are:

1. Michael Phelps: Probably the most searched on google for the past few days. He is even being considered as the greatest sportsman ever! not sure what criteria one would use for that but anyways, I read a few articles about him on BBC and other places. Here are a couple:

http://news.bbc.co.uk/2/hi/asia-pacific/7562840.stm
http://www.bbc.co.uk/blogs/olympics/2008/08/can_anyone_spoil_phelps_pool_p.html

So after reading his routine, I was like no way would I be able to do something like that unless I am motivated so much by the fact of winning medals at olympics or becoming famous or whatever motivates him. Plus for those who consider perseverence trumps talent, check out his physical structure, thats in born - I dont think perseverence can trump something like that. He was probably trained right from young age to be what he is today. All he does is eat, sleep, swim. Can you imagine not being able to eat when you want, what you want, have no routine, take one day at a time. I can't imagine training like that most of the year or even more than a year leading up to the olympics or whichever other event he is taking part in.

This was just one such extreme example, but I guess it applies to a lot others in various other fields. To be really famous, one has to be extremely dedicated, determined and disciplined + has to have the talent.

2. A friend of mine who has been working for the past 15-20 years at the same place doing pretty much similar work. Grew up in the same neighborhood where he works, has his year planned out to do different things at specific time in year. He is married with kids, hopefully enjoying his life with all the +'s and -'s it comes with. Should he have strived harder to become something more than what he is today? Should he regret as to why he didn't push himself enough? should someone else have pushed him more? was it circumstantial that he would not have been able to? Or he is just happy the way he is and has nothing to complain about enjoying the little things in life!

I guess where I am heading with this argument is at what point in life does one decide how much to strive for and what to strive for? Is there an end? a limit may be? Should one be concerned about the society he/she lives in and strive accordingly to live and match up to it, if he doesn't can he/she still survive? with ever rising prices of everything, should one be considered as to how much is enough? is there a target? Would I be regretting if I didnt lead a company one day? would I regret of not giving my best if I just keep chugging along as I am now? Each day passing by is telling me "there goes one more day and not much has changed!..." should each day really change from the previous day? should I just give it time, put my best foot forward and leave the rest? if so, how do I know whats my best?...........................