Never open the door to a lesser evil, for other and greater ones invariably slink in after it.

Baltasar Gracián (1601–1658), a Spanish Jesuit and moralist of the Baroque era, wrote in a culture preoccupied with prudence, reputation, and the management of risk in courtly and political life. The sentiment fits the practical, aphoristic counsel he offered to readers navigating temptation, compromise, and the slippery logic of “small” concessions. In Gracián’s world—shaped by Counter‑Reformation ethics and the hard realities of Habsburg Spain—moral and strategic lapses were often framed as openings that invite further corruption or danger. The image of evils “slinking in” reflects his characteristic style: vivid, cautionary, and oriented toward self-governance.

The aphorism warns against rationalizing minor wrongdoing or “acceptable” compromises. A lesser evil, once admitted, changes the moral and practical boundaries of what one will tolerate; it normalizes the breach and makes subsequent, worse choices easier. Gracián’s metaphor of a door suggests agency and threshold: the first concession is the decisive act, because it creates access and precedent. The line can be read ethically (guard conscience; do not bargain with vice) and strategically (small risks can cascade into larger harms). Its enduring appeal lies in its psychological insight about habituation and escalation.