Unlike some 3D software, Blender doesn't keep any construction history for objects or operations. This has the upside that our objects are always ready for the next operation to be performed, but it also has the downside that previous operations will be final as soon as we move on to the next operation. This is known as destructive editing.
Even performing small adjustments, such as transforming or deselecting, will apply the previous operation. All of the settings will be committed to the object and can no longer be adjusted. When working with destructive operators, you must set the settings correctly in-the-moment since you will be unable to change them after-the-fact.
Up to this point, we have modeled the chair with destructive editing methods, but in the next step, we can use some non-destructive editing methods for a...