Sometimes I can't help noticing that we live in a world where everything is quantified, so the notions of success and achievement are based on measurements, typically in an attempt to be (quasi)scientific in one's approach to training. While such a view has some value in certain domains, particularly in a professional sport field, I believe that in some other practices it might be (at least occasionally) harmful.
Even in a very streamlined sport of weight lifting, for example, there are so many factors involved (sleep, mood, state of health etc.) that it would be ill-advised to focus on the numbers as the sole indicator of progress. More than once have I seen a lifter miserable after a good session, because they failed to reach a goal that was a number on the paper (or the screen). How do you quantify quality or pleasure?
Things get even more complex in an oppositional skill based arena that is martial arts and combat sports. For a lot of people involved in these, there is this idea of making progress by "getting to the next level", which entails learning advanced techniques and/or more new maneuvers. You see it everywhere, from the modern BJJ and MMA gyms and their new tricks of the trade, to the traditional schools, where the new belt means new forms and techniques. We always strive to get to a new step and climb higher on the chosen ladder of success.
But what if that is a wrong viewpoint? After all, they say that advanced techniques are the basics done really well, right? Wouldn't that mean we ought to get deeper, not higher? Hey, even the Earth's structure prefers depths to heights!
"...but often better than the master of one!", however! Wait, what? Aren't I contradicting myself? Well, not really. See, IMHO, one needs to be a comprehensivist in terms of areas of competence, but then a deep diver in each of them. Naturally, the number of those areas of competence will depend on your purpose in training - sport, cultural study, recreation etc. Let's say you are a MMA practitioner with competitive inclination: you would need to develop some functional skillset in standup/striking range, clinch/wrestling and the ground/grappling game. Now, if you have previous background in one of the disciplines that are typically perceived as "main ingredients" of MMA (i.e. (kick/Thai)boxing, wrestling, judo, sambo, BJJ), it could be possible and maybe even recommended to build a strategic approach of taking the fight to your area of expertise, with solid defense in all the others.
Let's see what the deep dive consist of, then. The first thing would be to identify a finite set of techniques and tactics that make the functional foundation within that area and then work on truly internalizing and integrating them, to a degree that we could improvise and play with them at will. For example: in the standup game - jab, cross, front hook, low kick and (maybe) front kick, corresponding parries and defenses; in the clinch game - a couple of controls and takedown from wrestling (underhook, weezer, single leg), head/neck control and a couple of elbow and knee strikes from Thai-boxing, takedown defense/sprawl; on the ground - essential positional control, 2-3 escapes for each position, 2-3 submissions from each position, a couple of fundamental sweeps/reversals, and fundamental ground and pound options.
Huh, it is still quite a bit... But, if you get deeply skilled in those, there will almost certainly be no need for jumping or spinning kicks and backfists, scissor throws and suplexes, berimbolos and lasso guard or calf slicers. Leave those to the folks specializing (i.e. deep diving) in those singular disciplines.
If your aim is on the pavement arena of self-protection, you will also want to address hand held weapons (impact and edged...firearms if it fits your legal environment), with emphasis on access and deployment, along with a couple of low-risk and effective techniques/strikes, while discarding the twirling and flipping stuff. (There are quite a few reviews of the applicable instructional volumes on this blog). When it comes to defense, focus on control over disarming. While on the subject of street self-defense, if you try running a couple of scenarios that involve multiple attackers, it will quickly become obvious which physical techniques and tactics are to be prioritized (footwork, standing wrestling, straight punches, low line kicking).
Thanks to the easy access to video footage of all kinds of physical situations, it is relatively easy to figure out what are the technical and tactical tools that should be prioritized, so-called high percentage ones, in order to avoid straying away from your training mission.
After that, all you need is to dig in...deep!