What you said is really true.  In my case, my self investment is prioritizing my health.  I am trying to get enough and sufficient sleep always.  I also enrolled in a gym to have regular exercise (muscle training and cardio).  By taking care of my body, this will help me in a long run.  Also, back pain have been lessened since then.  I also encourage others to invest on yourself, one way is to take care of your body.