Incautiously

His behaviour to herself could now have had no tolerable motive; he had either been deceived with regard to her fortune, or had been gratifying his vanity by encouraging the preference which she believed she had most incautiously shewn.

[…] the piranhas habitually attack things much larger than themselves. They will snap a finger off a hand incautiously trailed in the water […]

The parson explained that the dissenters were insufficiently grounded in religious learning, inappropriately eager to administer the sacraments without his help or sanction, and incautiously emotional in their worship.