Why ? Because it's going to kill your day. You need to take some distance from the events affecting you to see the humour into it. You need and this is the hardest part to let go of your need for control and accept that in certain cases laughter is your best weapon to move on. Of course I am not telling you to laugh if you have a relative sick or seriously injured.
No, what I am saying is learn to appreciate what each circumstance, event will bring to you, not only knowledge, strength but also this ability to laugh of the irony of some situations in which you got involved. Of the strictness of some of your rules, ways to be which can be either debilitating or simply limiting your true potential.
Laughing is another version of letting go. Move on without resentment, anger and freeing yourself from the past to live in the moment and build your future.
Taking it easy is being kind with yourself, avoiding setting unrealistic goals to kill your mojo and enthusiasm.
Taking it easy is being smart, smart to step back, observe, listen to your inner voice and act on it.
Not taking yourself too seriously is letting your humanity breathe, accept your imperfections and work at your pace to be the best version of yourself. Every goal is taking time to be reached , it's much more clever taking time to plan it than beating yourself unnecessarily when you do not see any results after two days...seriously.
In a nutshell, if you want to reach a goal for this year, be smart about it and allow yourself some "me time" or treat (when you need it) before to get back on the road to make your dream come true.