That's mean you‘re not a hundred percent sure about something

不能把握 implies that you are not able to do something 无十足把握 indicates that you are not confident that you'll accomplish it, though actually, you might be able to do it.

无十足把握就是不能百分之百保证他们能做到。

十足=十成=100% 就是：不是100%的把握

不對！不能把握是完全（100%）無法做到，無十足的把握，是做得到但機率可能只有五成以上！