Is refusing to participate in da'wah to Allah in the street—due to not feeling ready—considered a sin?

"Da'wah (inviting to Islam) is through words and actions, and it has various methods. A Muslim must undertake da'wah if he is capable of it and no one else is doing it, or if what others are doing is insufficient. Among the methods of da'wah are: seminars, lectures, admonitions, sermons, writing, audio recordings, magazines, and good character."