"Do things together. Don't do things apart. Pursue together."
Sarah and I are passionate people. We're also pretty good at what we do. The quote holds true: "You can go faster alone but farther together."
How the heck does this relate to the "spark" in marriage?
Sarah and I don't work together. That's 33% of our day.
We sleep. That's 33% of our day.
If I grow in an area away from Sarah (poker night with the guys, building a side business with a friend, business networking without her), there's very little we REALLY share together. That last remaining 33% of my day isn't invested in our relationship. Sure, it may be invested in growing our finances to pay for family needs, or pursuing fun (even noble) things, but the FACT is we're not together.
When I get to see her (in person) experience cool stuff, and I'm also invested in that stuff, we build memories. When she gets to see me train and race, endure the day-in day-out swim/bike/run sessions, we build memories. There's something extra special about really sharing what matters most to us with each other.
This leads to plenty of sparks.
What takes away from sparks is growing apart from Sarah.