Short answer? We stay motivated b/c being poor when you are old sucks, as we are daily reminded by friends and family.
Long story:
My husband and I were pretty decent with money, never carried regular consumer debt, kept college costs low, etc. But we also got started 'adulting' very late. My husband is the primary earner and was 39 before he got his first 'career track' position after growing up poor, finally going to college in his mid-20s, and getting multiple advanced degrees. I'm 9 years younger, but have always worked the gig-type economy with no benefits (for reasons too long to go into) and modest wages. So we missed a good 15 years of prime savings window. Then we further frittered away 5 or so years accumulating the house, car, furniture (we didn't even own a bed until he was 39), paying off the student loans, etc., before getting really serious about our finances. And even then, about 10 years into adulting, we started partially supporting parents as well, which further limited cash flexibility.
Even so, once we really began prioritizing no/low debt and retirement savings (and keeping cost of living low), we were able to make very good progress. We went from about minus 150K net worth in 2001, to about 0 net worth in 2007 (after buying second house and car and taking on parental support), to closing in on a million, likely sometime next year. And that's net worth of which <20% is real estate value; it's mostly investments.
Realistically, my husband won't be RE, but he loves his job so it's not that big a deal. What keeps us motivated is reaching FI, that point of minimum security where if one or both of us HAD to stop working, we could keep a decent lifestyle. Both our families have a lot of poor, struggling people, and that lifestyle sucks. We don't want any part of it. We're currently on track to reach minimum FI at his age 60-62, and more 'lux' FI every year after that that we want to keep working.