Let me spell it out:
N is the number of communicative civilizations.
R is the rate of formation of suitable stars. Can we closely estimate this number? No.
fp is the fraction of those stars with planets. Can we closely estimate this number? No.
ne is the number of Earth-like planets per solar system. Can we closely estimate this number? No.
fl is the fraction of planets with life. Can we closely estimate this number? No.
fi is the fraction of planets with intelligent life. Can we closely estimate this number? No.
fc is the fraction of planets with communicating technology. Can we closely estimate this number? Not in a million years.
L is the lifetime of communicating civilizations. Can we closely estimate this number? No.
Because we don't know doesn't give credibility to the equation.
N is the number of communicative civilizations.
R is the rate of formation of suitable stars. Can we closely estimate this number? No.
fp is the fraction of those stars with planets. Can we closely estimate this number? No.
ne is the number of Earth-like planets per solar system. Can we closely estimate this number? No.
fl is the fraction of planets with life. Can we closely estimate this number? No.
fi is the fraction of planets with intelligent life. Can we closely estimate this number? No.
fc is the fraction of planets with communicating technology. Can we closely estimate this number? Not in a million years.
L is the lifetime of communicating civilizations. Can we closely estimate this number? No.
Because we don't know doesn't give credibility to the equation.