If fitness, athletics, or aesthetics are your goal, there is nothing that should be unexpected. I don’t think that you have to be ready for “anything” but you do need to be ready for exactly what you want.
Traditionally, planning for your training means periodization. In some form or the other (undulating, conjugate, linear, etc) periodization can help you achieve that goal.
My view on periodization has changed a lot in the last 15 years or so, but so have my views on Brussels sprouts, professional wrestling, and how to get women. While 16 year old me thought that every rep had to be planned out to a T, Brussels sprouts sucked, Goldberg was the pinnacle of man-dom, and chicks liked it when I called them “chicks,” 31 year old me knows that there can be a little wiggle room in the master plan.
Today I have a better understanding of how to REALLY use periodization to get the best out of my program