We can't ignore the importance of things in our life. A man needs different things in his life according to his age and requirements. It is not necessary that you need same things in different parts of your life. Childhood has different demands; youth has different demands while old age demands different things in the life of a man. So far your question that how things get important in life, can be explain like this.
When a child is born, he requires assistance, cooperation, and love from his mother. At that stage he needs milk, cereals, juices, and light foods. When he grows young he starts eating different things like meat, chicken, beef, other poultry items, tea, coffee, fruits, soups etc. In short youth is the time in man's age in which he can enjoy all the edibles available. He likes to wear good clothes and enjoy different things. Old age is the age of responsibilities and one does not require things like his childhood or youth. A man requires less food, less clothing and lot of medicines due to different diseases, which overcome with the passage of time and old age. So we can say that different things get important in different stages of life.

 Life is full of challenges. It's our temperament of doing things that how we deal with the problems. Change is the spice of life as soon as we grow up our demands towards life start changing.
If we talk about our childhood at that time child is only going through the things like, only food or milk are his priorities, in school period his way of looking at thing is different. And in his young age life again takes turn. Now he looks toward things in quiet a different way now he is more interested in hanging out with his friends, playing different games, studies or job, after marriage life its totally changed again.Now there is a cycle in our whole life form our childhood to our old age we are continuously passing through changes, they are automatically coming in and out of our life.
And same is the case with the old age, we have different personality at that time our priorities of life changed .We are more concerned about taking our medicine on time and our rest time. So changes and things are always coming in out of our life ,and things by there self get importance for us in different phases of life.