Some encouragement for those just starting out with low numbers that feel they are missing something...
When I began fly fishing and for about 10 years afterwards, my quiver contained a 5'0" 4wt (graphite), 7'6" 5wt (graphite) & an 8'6" 6wt (graphite). With those three rods I fished EVERYWHERE including SEPA, NEPA, SCPA, NCPA, Catskills, NYC reservoirs, Northern Joisey; you name it...
Later I sold the graphite rods and bought a 7'0" 4wt (bamboo, 8'0" 6wt (bamboo), 8'0" 4wt bamboo, 8'6" 7wt (bamboo) & a 9'6" 8wt (bamboo) and fished ONLY those rods for almost two decades before beginning a serious acquisition phase almost 20 years ago when I had the cash and desire to revisit graphite and discover glass.
HOWEVER, before I went nuts, I honestly never felt like I NEEDED more than three or four rods for the kind of fishing I did with a fly rod which was close to 100% trout in PA, NY & NJ.
Obviously it helps that when it comes to bass or the salt, I'd rather use spinning or casting tackle because I HATE fishing with big flies on heavy lines and I'd rather target sunfish with a bobber & worm; but the reality is...
If you stick to one or two types of fishing and/or types or sizes of water; two or three rods will easily get the job done. If you are a just brookie fanatic or medium stream aficionado, you could probably get by with one rod.
I readily admit that if you have the desire & funds, having a rod or combo for every mood is lot more fun, but hardly necessary.