In a high school electronics class, we built our "7-transistor, super-heterodyne, pocket AM radios" from a kit. The built-in speaker (about two inches in diameter) was poor, the hard plastic earpiece for "personal listening" was even more inferior. But, dating myself again, the good music was still on AM and we had little frame of reference for quality.
A very short time later, I had what I considered a "great" set of Sonic (a brand you probably never heard of) three-way monitors, but also a set of Pioneer open-ear headphones that actually sounded better than the speakers. I cannibalized an old all-in-one turntable/AM/FM console of my Dad's to build my next set of speakers, scaling up the dimensions of the Sonics for a home-built cabinet to house the larger components. They sounded a lot better once I realized I needed to install a crossover, I quit over-tasking my 40W X 2 JVC receiver with the parallel speaker load, and I updated the woofers. That set of speakers (once suspended from the ceiling in a homemade macramé hanger — it was a different time) was foisted off on a mover some time ago.
After my Pioneer headphones died, it was some time before I actually thought of headphones as musical once again. That didn't start in my early years in broadcast; I inherited a drawer full of DJ-abused Koss 4A phones and I continued to repair them (replacing blown drivers, ripped wires, earpads stiffened rock-hard and so on) for the next six years. I won a set of pro open-ear phones in a contest, but the rigid head piece made me feel like my ear drums were touching, even though they sounded pretty good till the pain set in. A set of AKG K240s was the first of my second generation of positive experiences with headphones, prolonged and continually improved to the present by a parade of Fostex, beyer, Sony, Sennheiser, more AKG, Ultrasone and Audio-Technica models.
I didn't consider in-ears viable (I tried various ear buds that came with portable electronic devices till I eventually quit even unwrapping them) until my first set of Shure universal earpieces, followed by other Shure models, Future Sonics EM3s then Atrios and, most recently, a set of custom-molded Sensaphonics in-ears. After a set of Genelec S30Cs became my shop speakers in my studio days, there was no going back to consumer models, and I currently have monitors from Tannoy, Genelec, Alesis, and JBL at my disposal, along with a string of review monitors that come and go.
If there's actually a message to be found in these reminisces, it's simply this: Life's too short for bad monitoring. Don't wait, don't compromise; investigate and invest. Everything you do as an engineer depends on what you hear.