As someone who keeps 401k 100% in sp500 that scares me. If the bubble pops it will erase half of gains, if the bubble continues then the gap(490 vs 10) will gro

As someone who keeps 401k 100% in sp500 that scares me. If the bubble pops it will erase half of gains, if the bubble continues then the gap(490 vs 10) will grow even larger.