When we become parents we want to be there for every special milestone and moment in our baby's life. But while today's mothers are spending more time with their children than the generations before us did, but we're also spending more time on paid work. So as much as we would love to be in two places at once, we simply can't be. And sometimes, that hurts.

It's a reality Serena Williams understands. She recently missed a milestone that many mamas look forward to witnessing: Her baby's first steps.

"She took her first steps... I was training and missed it. I cried," she tweeted Saturday.

It's totally understandable that Williams was heartbroken to miss this milestone in baby Olympia's life, but it's a pain many mamas can relate to.

According to the results of a survey released by Motherly , 78% of mothers surveyed say they have mixed feelings about combining a career and motherhood, and that "there are real tradeoffs".

Missing your baby's first steps because you were training to compete as an elite athlete or because you were working a desk job could be considered a tradeoff of working motherhood but Williams and other moms should absolutely not feel guilty about missing a milestone while they're working (as Twitter users pointed out).

The truth is, missed milestones aren't just a hazard of working parenthood, they're a reality of parenting, period.

A stay-at-home mom might learn her baby took their first wobbly steps while she was taking a quick shower or loading the dishwasher. A co-parenting mother might learn her baby stood for the first time while they were at their other parent's house. A mom or dad might send their child to spend the afternoon with grandma, only to learn baby's first word came while they were finally getting a desperately needed haircut.

It's heartbreaking when this happens. It's absolutely natural to feel disappointed. It's understandable to cry like Williams did.

It's hard and it hurts and that's okay but it is not your fault, mama.

Parents should try to be kind to themselves when this happens. Because it happens all the time, and (like Twitter users pointed out to Williams) even to parents who don't work outside the home.

When a milestone is missed, take the advice of psychologist Eileen Kennedy-Moore, who told Working Mother that "milestones are not a single moment."

"You may or may not be there the first time your child stands, but you will definitely have a first time when you see her stand," she says. "That is the moment to celebrate and share in your child's joy."

Williams' daughter Olympia will take more steps, and Williams will get to see them. And the steps she takes for mama will be just as special a moment maybe even more special than the moment Williams missed.

We can't be there every single second of every single day. But we can make the most of the moments we do get. They're the special ones.

[Correction, July 7, 2018: An earlier version of this post contained a photo of Olympia with her aunt, Venus Williams.]