When looking at FPTP results for electing a parliament or legislature, one often sees that party A received some percentage of the so-called popular vote, party B some other percentage, and so on, which percentages might well not be reflected in their aggregate seat count.
There’s a natural tendency, then, to think that the respective parties should have got that same percentage of the seats, i.e.: that the number of people elected from each party should be proportional to their party’s portion of the total vote. That they generally do not often fuels perceptions of disenfranchisement, and the sense among many that the system is “broken” and that their votes don’t really count.
While many people who at this point cry out for proportional representation really do want proportional presentation, a great many of them are really only looking for something better than FPTP, and aren’t really aware that there’s an option besides the “proportional representation” that they keep hearing about.
In any case, while not in agreement with the call for proportional representation as a resolution to this perceptual dissonance, I do recognize the feelings of futility and disenfranchisement that drive it.