Before making the current startup successful and devoting maximum time to this and valuing this true experience; thinking of an another startup and working on it can become suicidal. This can become a precise example of over confidence.
One may face hurdles but this is what one should learn while on the journey to become a successful Entrepreneur. It is not a good thing to think of starting another startup as hurdles will come there as well. Its better to learn from these and make oneself experienced in handling the situation so that it adds to the skills.