What haven't I built... The most difficult and yet easiest thing was the relationship to Lily. Difficult because all the boulders that were laid in my way, easiest because it just was so natural to overcome them by any means necessary.
The business was very hard to build, and it had many setbacks within the time. Still has. Although I just recently started studying Stoicism, one rule I always applied - building it on who I am and wanted to be, a business based on my principles. That made every decision easier.
Talking about, that also caused me to destroy. Building the business severed my marriage. And my relationship to some people. Jealousy was always a thing, and sometimes misconception, for not asking me but assuming, or worse, listening to gossip. I don't mind having lost those connections. Those who indulge into jealousy and gossip are not relationships I want to have, anyway. And the connection to my ex-wife is quite good now again.
And as for opportunity - a mix of everything. Always looking for it, always creating some, and I did get lucky once or twice.
RE: Your building