You Don't Deal Well With Unexpected Changes to Your Schedule
Life is unpredictable. No matter how we try to plan or schedule around it, the one thing that is constant is change. Having enough temporal breathing room in your life means that if someone can't make a pickup or a meeting gets moved, you can respond and adjust with some amount of ease. If your response instead is more along the lines of hyperventilating and making a beeline for your Google calendar, then you're probably too tightly scheduled.
Try this: Make sure to build in at least 15 minutes of cushion time between all scheduled appointments to allow you more flexibility to adjust to changes. Your daily schedule should also ideally have a mix of critical and non-critical appointments (i.e. mix a pedicure with a review with your boss), instead of back-to-back appointments of high importance, so that if something unexpected happens, you'll have more flexibility to move things around.