Progression is absolutely vital for success but might look different then you think.
DIFFERENT TYPES OF PROGRESS
Progress is what we want from training. If there's no progress it's bascically just movement - not training. But progress is not just increasing weight. Progress in training has many faces. Progress is small improvements that you should strive for in every training session. Here is a list:
Weight
Number of reps with same weight
Number of reps in shorter time
Longer time under tension
Better technique
More range of motion
Faster bar speed
WEIGHT (OR INTENSITY)
You can either increase the intensity (weight, speed, etc.) within an exercise or the intensity of the whole workout.
REPS & SETS (OR VOLUME)
You can increase volume (sets, reps, distance) while keeping the intensity the same.
REST TIME
Both the time between the sets but also between the exercises or the whole workouts plays a role in the subject of progress. Of course, it depends on what training phase you are in and what specific goals you are pursuing. But doing the same or more work in less time is progress.
TIME UNDER TENSION (TUT)
TUT refers to the amount of time a muscle is under tension during a training set.
TECHNIQUE
Squats, deadlifts, bench press, olypic lifting - these movements can be optimised. They are also a skill that can be learned and improved. Performing the same weight with improved technique ist progress.
RANGE OF MOTION (ROM)
Studies on range of motion and its effectiveness in building strength and muscle are mixed. Some muscles, including biceps and leg extensors, seem to benefit particularly from full range of muscle stretching. Working thorugh a larger range of motion than before is progress.
BAR SPEED
Bar speed is a great objective tool to measure progress. If you can move the same weight faster than before - that's progress.
As you can see - progress is not just about adding weight. Progress can come in different forms. Don't get discouraged if you can't add weight every session.