How heavy do you think this bottle of water is? 

It's not the weight of the bottle that matters, it's how long you hold on to it. 

How long you hold on to it can create the pain. Like lifes worries and stresses. 

If you hold on to them for a minute, it's OK. If you hold on to it for 2 days, 2 week, 2 years it can be really detrimental to you and your health.