We are mortal.

In the world of college athletics, this is sometimes easy to forget as a Stanford student. With 19 consecutive Directors’ Cups, three consecutive BCS berths, an absurd number of national championships and an impressive haul of Olympic medals, it’s rare to feel outmatched and hard not to feel invincible.

But over the past few days, I’ve received a few reminders — some way too bitter — that we are not invincible.

On Wednesday evening, Stanford announced that fifth-year senior men’s basketball player Andy Brown would miss the upcoming season with a torn ACL, the fourth ACL tear of his now-finished college career.

Obviously, after three ACL injuries, Brown knew he wasn’t invincible; yet with the progress he had made and the expectation of success, I assumed his story would end in triumph on the court — that’s what he deserved. Unfortunately, that won’t be the case.

Then on Thursday, I received another reminder, though not as harsh, of how even the most unbeatable Stanford student-athletes can eventually face tough times when I watched Nicole Gibbs’ second-round tennis match against Jamie Hampton at the Bank of the West Classic.

In her three years at Stanford, Gibbs, a fellow member of the Class of 2014, had been dominant. As a freshman, she was a singles All-American. As a sophomore, she won both the NCAA singles and doubles titles — she beat her doubles partner Mallory Burdette in the singles final right before their doubles triumph.

But her peak came in her junior season this past year. As team captain, Gibbs led Stanford to upsets in its final four NCAA Tournament matches to win the national title, keeping Stanford’s NCAA Championship streak alive in the process. Then Gibbs took home the singles crown for a second consecutive year before leaving school for the professional tour, as she had planned to since the fall.

Watching her compete throughout that time, I thought Gibbs was unbeatable. Sure, she was capable of losing a match, but I never saw anyone in person who I thought could actually beat her when Gibbs was playing well.

I saw one of those people on Thursday in Jamie Hampton.

Hampton is the No. 29 singles player in the world. Her serves and groundstrokes have tremendous power and her net game is extraordinary. She looked like someone capable of ascending to the top of women’s tennis.

Gibbs, to her credit, put up a remarkable fight. After dropping a close first set, Gibbs battled to stay in the match. When the second set went to a tiebreaker, Gibbs buckled down and evened the match, sending the fan section of seven Stanford football players into a frenzied cheer.

I thought it was over in the third set when Hampton came out with a fire we hadn’t seen all match to take a 4-0 lead. But Gibbs clawed back again, getting it back on serve at 3-4. Eventually, though, she couldn’t hold her serve and lost the match.

I know that’s probably more detail than you need for this column, but I want you to see how much of a fighter Gibbs is. And on top of that, as the two-time defending NCAA singles champion, she is tremendously skilled.

Yet Gibbs was the less talented player on the court on Thursday.

There’s no shame for a 20-year-old who just turned pro to be less talented than a top-30 player, but it’s still tough to get used to.

With the exception of Andrew Luck, Gibbs’ story is common. Stanford student-athletes may dominate in college, but there is another level of competition out there that is even tougher than the Pac-12 and NCAA. Even Toby Gerhart has yet to crack an NFL starting lineup — not that being Adrian Peterson’s backup is anything to be ashamed of — and he was perhaps the best runner in Stanford history.

So while we will all continue to enjoy the most successful period of Stanford Athletics in recent memory — as we should — let’s remember that there’s still reason to stay humble.

A fluke injury can take out the most courageous among us.

A great player can take down an NCAA Champion.

Sam Fisher is having issues coming to terms with his own lack of athletic invincibility after he lost in the first round of the Daily’s annual thumb war tournament. Tell him that everything will be okay at safisher ‘at’ Stanford.edu and follow him on Twitter @SamFisher908.