We have heard the term 'having the benefit of the doubt'? When it comes to sport, it can be deleterious to our performance if we are not careful.
Doubts cast indecisiveness, apprehension, self-doubt and hesitation. Doubt can manifest itself through injury, lack of systematic training, poor preparation, fickleness, and the influence of others.
When doubts stem form oneself, review your plans and expectations. Be pro-active and make changes to improve and be better. When doubts come from others, pay some attention but not completely. When father knows best, he may only know what he knows. Mother knows better, too. If other people's doubts become your doubts, this inheritance may be costly to your investment; all that training, recovering and recuperating may come to nought.
Know what you doubt; be doubtful, but never over-doubt yourself.