discover or invent?

Today was just another ordinary day.. full of routine, of things I have to do, of promises to myself..nothing new of them, neither.. just the usual "from tomorrow I should go to bed earlier", " I ll start a diet to lose those extra kilos I long to get rid of", " I ll eat healthier ", " I ll spend less time in front of my PC" etc.. Sounds familiar? I think it 's more than hundreds of times I say that to myself..
Sometimes I keep to them for a couple of days if I m lucky.. But most of the times I forget about them as soon as the need comes again to my senses.. And I can't help thinking.. how much of me am I able to modify? and under what circumstances?
I remember my teacher of psychology in high school told us that humans can only modify their personality under major changes.. like a great misfortune, catastrophe, death of somebody dear..and the same opinion I read in one of my favorite books " The egyptian" by Mika Waltari. He stated that men have some typical features that are common to all and can't really change..Even if an awful thing happen and they say " now I see how miserable I can be, if ever I should recover from this trouble, I ll change my life completely!".. and when they do..they just start over again with the same old shit.. There are exceptions, of course..But unfortunately I am not one of them.
So, should I just accept that there are things which I don't like about myself and learn how to live with them ? and even start to see the good point in them ( supposing that they are )?.. A granted advantage of this would be the time I could use to enjoy the present moment and not live to wait for the next good things I would do.. But the reverse..not making any effort to improve, to defeat the weaknesses?
I remember of a quote I saw in the Stanford library.. " life is not about discovering yourself, but about inventing yourself". So, they also think we are able to do (almost) everything we long for? Are there limits in this process of invention?
Maybe the 'success' type people think like this..maybe when you don't feel there are barriers in your way, you have no limits in getting better?