You will not always be able to control some training variables.
Frequency. Every once in a while you’ll get sick. Every once in a while you’ll have to stay at work late. Things like these could prevent you from getting to the gym as frequently as you would like.
Duration. Some days you get caught in traffic on your way to the gym. Some days you have to pick your child up from school. These are things that could cause your workout to be cut shorter than you had planned.
Load. Maybe it snowed a lot today and your gym is closed due to the weather. Maybe you are traveling and your hotel gym only has a treadmill and a set of 5lb and 10lb dumbbells. These are times when you may not have access to the equipment and the amount of weight you are accustomed to training with.
But one thing you can always control is intensity.
(Training) Intensity refers to how hard your body is working during an activity.
If you were unable to work out some days this week, make sure to push the intensity on the days you are able to.
If your workout has to be shortened tomorrow, make sure to be as efficient as possible for the time you will be working out to keep the intensity higher.
If you aren’t at your regular gym and have to make do with lighter weights, use pauses or tempo, or extend sets for more reps to increase the intensity.
It shouldn’t matter how often you’re able to work out, how much time you have to work out, or what equipment you have at your disposal - you should always be able to find a way to push yourself to a proper intensity level.