The difference of reality and illusion of life is what keeps us present or not present. If you live with reality you will be present, if you deny reality you live in illusion and cannot be present.
The reality is; from the instant you are conceived, you are dying and going closer to your death.
With every step forward that you think you are making, you are growing, learning, acquiring more success, money, property, etc. You are moving towards your death. This is the law of opposites, everything is both at the same time. Every instant of growth is one instant closer to your death and leaving all that behind.
The law of nature is decay. Everything is decaying, sometimes at rates that are imperceptible to human eyes. Everything is in a downward spiral to its eventual dissolution.
You may not like it, but it is the reality. If you take the absolute reality that eventually everything is destroyed in its material form, even your life, and body, then the mundane things of life that trouble you, can no longer trouble you.
If something is temporary it is much easier to deal with in a detached manner than if it was permanent. What keeps you in illusion and separate from being present in reality is your illusion of permanency, ignoring the reality of the temporary nature of all things in material form.
When we accept the objective reality that every moment regardless of if you perceive it as growth or decay is leading to your eventual death, then everything is really fine because you are following the law.
As with any law, if you break it, you will be watching over your shoulder in case you get caught, and thus not looking forward or being present. But if you follow the law, you can be comfortable and relaxed.
Happiness and true living of life can only happen when we have no fears, and accepting reality is the way to remove all fears.