Concurrently accessing shared data from multiple goroutines without synchronization leads to race conditions. When goroutines read and write the same variable concurrently, the order of operations becomes unpredictable, resulting in corrupted state. Using mutexes from sync package to lock access ensures only one goroutine can read or write the shared variable at a time. Missing synchronization allows uncontrolled concurrent access that can cause intermittent bugs, crashes, and unreliable behavior.