Question

Why does hyperconjugation happens?
well i m not asking about any specific molecule.
what if I say that there is a molecule which is having hyper conjugation and I'm not allowing it to do so......

Answer 1

No, you can't allow or disallow that process, because its natural.

Hyperconjugation is the stabilizing interaction that results from the interaction of the electrons in a σ-bond (usually C-H or C-C) with an adjacent empty or partially filled p-orbital or a π-orbital to give an extended molecular orbital that increases the stability of the system.

It is nothing but the process to obtain stability, and it is the nature of anything in this universe to move towards stability.

If possible you can create another process such that the stability increases much more in that process than in hyperconjugation, then it will cease to happen, not entirely though because some percentage of molecules will go for hyperconjugation and that will depend of the probability of that event.