How do I adjust my business plan when reality doesn't go as planned?

You can make the plan. That already puts you ahead. What trips you is that reality never follows the plan, and adjusting on the move feels like failing. It is not. A plan that meets the real world and bends is doing its job. A plan that cannot bend is the one that breaks. The mistake is treating the plan as a promise instead of a guess. Every plan is your best guess at the start, made with less information than you have now. When reality pushes back, it is handing you better information. Changing course is not abandoning the plan; it is using what you have learned. The good ones expect to be rewritten. Build in a rhythm for it. Once a month, sit with your plan and ask one question: what did I learn that the plan did not know? Then change one thing to match. When adjusting becomes a regular habit instead of an emergency, it stops feeling like defeat.