This is popularly known as instability. If you have problems climbing stairs fast, running, jumping from height and playing sports, this is likely sign that you require a surgery. ACL is supplemented by muscle cover and joint capsule which help provide stability. also while walking, pivoting or rotational stability is not demanded, which happens to be the cheif function of ACL. So, better get it done early than to suffer irreversible cartilage damage in the long run.