The first question you have to ask yourself is whether marketing and selling products is something which you are comfortable with. There are many people who think they can withstand the hardships of this profession, but start having second thoughts as soon as they get rejected for the very first time. If you are one of those people, you are definitely not doing yourself any favors. You have to have a very thick skin in order to survive in this field.
Even if you have strong wits, ask yourself whether you really enjoy this line of work. If yes, where do you stand? How is your career progressing? Is it at a place which you had envisioned? And if not, what are the reasons behind it? Analyze your comfort zones and the aspects of marketing which make you sweat. Ask yourself whether you are willing to challenge yourself further. Remember, you are the best person to judge yourself.
The best way is to set goals for yourself, and take small steps rather than aiming for the stars. There is no easy path to success and whether you experience success or failure, maintain a high level of confidence, self-esteem, ambition and a will to succeed at any cost.