To draw home the point let's take a simple analogy. Consider a garden. As you know, in that garden weeds will grow whether you do something or nothing in the garden. But if you want to grow a flower you have to look after it with care, water it, make sure the weeds don't come near it and give it's needed nutrients.
If you don't do this time and again, the flower will die eventually. Even if you do it sometimes it may still die, but for the weeds if you don't clear them out, they will always, always be there and needs nothing of your care to grow.
So, if you want your garden to blossom, you have to clear all the weeds and take time to plant and look after all your flowers, time after time. But if you do that you will have a beautiful garden, where birds and butterflies will have a time of their life.
Negative thoughts are like the weeds and are quite bound to be there in all of us. Therefore we have to nurture positive thoughts to fill our minds, time and again. If we do this often enough, then we will have a mind full of positivity, which in time will not only be beneficial for us but for our friends and families as well.
