Jesus tells his disciples that they don't even have faith as big as a mustard seed:
Τότε προσελθόντες οἱ μαθηταὶ τῷ Ἰησοῦ κατ᾽ ἰδίαν εἶπον· διὰ τί ἡμεῖς οὐκ ἠδυνήθημεν ἐκβαλεῖν αὐτό; ὁ δὲ λέγει αὐτοῖς· διὰ τὴν ὀλιγοπιστίαν ὑμῶν· ἀμὴν γὰρ λέγω ὑμῖν, ἐὰν ἔχητε πίστιν ὡς κόκκον σινάπεως, ἐρεῖτε τῷ ὄρει τούτῳ· μετάβα ἔνθεν ἐκεῖ, καὶ μεταβήσεται· καὶ οὐδὲν ἀδυνατήσει ὑμῖν.
Then the disciples came to Jesus privately and said, "Why could we not cast it out?" He said to them, "Because of your little faith. For truly, I say to you, if you have faith like a grain of mustard seed, you will say to this mountain, 'Move from here to there,' and it will move, and nothing will be impossible for you." (Mat 17:19-20 ESV)
If a mustard seed is chosen as the smallest thing/seed they know of, is this a suggestion that "any less would be nothing at all? Or would it have been understood that an ever more minuscule amount was possible?
Is this why in some manuscripts ὀλιγοπιστίαν is replaced by ἀπιστίαν?