Put it this way... if your a true Catholic that's not optional.
if you ignore it and eat whatever you want, it's a sin. (NOTE: if for example... you honestly forgot and happen to eat meat during lent on a friday then there is no sin committed but if you know your not supposed to and ignore it, and do it anyways, then it's a sin. I have honestly forgot once in a while in the past but in general that's quite uncommon ill slip up like that. it's been years since I last slipped up like that.)
with that said... I am sure a lot of Catholics follow it because places like Wendy's fast food have fish sandwiches on their menu during lent where as normally they are not available throughout the year. so for a major fast food place to do this, then obviously they recognize it benefits their business and that means there has to be plenty of those selling during lent.
also, ill add... a lot of people are basically Catholic in name only but don't pray regularly or go to church on a weekly basis and holy days of obligation etc. basically they might have a general belief in God but that's about as far as they go (while this is better than nothing, it's clearly not up to the minimum standards of the church (hell, to be honest I was there for roughly 12 years of my life(i.e. believed in God but that was about it as i rarely prayed etc))). in other words... they are not 'practicing Catholics' which is what you really need to be doing if your going to claim your a Catholic and believe what the church teaches on morals etc as they are not wrong even if we don't like to hear it sometimes. like they are there not to penalize us (even though it may seem like it at times) but to keep us on the right path that leads to God/eternal life.
or another thing... looking around online it says there is about 1.2billion Catholics worldwide but I would estimate that in terms of 'practicing Catholics' it's quite a bit less than that given what I mentioned above.
for the record... I am not claiming to be all holy etc, as I am sure there are people out there far more holy than myself(I know I am no where near Saint level because I am a bit too selfish etc), but I am trying and chipping away a little here and there
; plus, another thing... it's like the more you learn the more you realize you don't know. so while I guess I could say I get the gist of the Catholic faith I still have plenty to learn and it will take decades and I likely still will have more to learn etc.
just some thoughts
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but one last thing before I go... for Catholics reading this, pray the Rosary every single day. it's basically the highest form of prayer outside of the Catholic Mass. or I could say the Rosary is the highest form of personal prayer.
p.s. you can't ignore official church teachings like having sex outside of legitimate marriage or that you cannot use contraception (i.e. condoms/birth control etc) etc which I suspect a lot of "Catholics" conveniently ignore even though it's clear cut sin and a serious sin at that which makes it that much more offensive to God (but honestly, I am not surprised that most people sin in relation to sexual desire because the sexual desire is one of the most powerful feelings we have that pretty much effects everyone). with that said... I realize a lot of people won't like that and will ignore it because it inconveniences them (like when they can't use condoms etc) but it's the truth. also, I am willing to bet that those who take what the church says more seriously and pray regularly are much more likely to follow what the Catholic church teaches than those who basically believe in God but that's about it and rarely or never pray and rarely or never go to mass etc(you get the gist). regular prayer is not optional but required if one is going to grow closer to God. you can basically see regular prayer (as in daily prayer) like this... oxygen is to the body like prayer is to the soul. basically helps sustain life within your soul to stay on the right path that leads to life etc.
side note: even when I was not praying or going to mass etc for that 12 years or so time span... surprisingly, I still stuck to the lent practice.