As Dr. Shad Helmstetter explains in his book What to Say When You Talk to Yourself, when we tell ourselves that we "should" be doing something, we're implicitly reinforcing the idea that we're not doing it.
Dr. Shad Helmstetter Ayaa buuggiisa 'What to Say When You Talk to Yourself' ('Waxa ay tahay in aad tidhaahdo marka aad naftaada la hadlayso), marka uu ka hadlayo 'Anshaxa' waxa uu ku qeexayaa, 'Habdhaqan, waa waxa aynu samayno ama waxa aynaan samayn.