There is some self-interest behind every friendship. There is no friendship without self-interests. This is a bitter truth.

The saying frames friendship in starkly realist terms: even the warmest bonds are rarely free of benefit, expectation, or reciprocity. “Self-interest” here need not mean crude exploitation; it can include the desire for companionship, loyalty, protection, status, or mutual aid. Calling it a “bitter truth” suggests a deliberate stripping away of sentimental ideals in favor of clear-eyed social psychology—an outlook often associated (rightly or wrongly) with “Chanakya-nīti” style maxims about prudence and political life. Read charitably, the point is not to deny affection, but to warn that relationships are sustained by incentives and can change when those incentives disappear.