In reality, lesson planning is one of the least certain tasks an educator undertakes. The lesson planner can be sure of what they intend to teach; it may even be articulated in measurable learning outcomes (the value of which is dubious). The teacher also believes they know how to present the material so that students achieve those outcomes. Further, they believe they know how students can best demonstrate what they learn. Other than the intended outcomes, planning is grounded in predicting (I think “guessing” is a more accurate verb) how students will be learning from the intended lessons and the degree to which the assessments will capture the intended learning.