The only thing I can be certain of its existence and even this not fully is that I exist. This is what the great philosopher Rene Descartes meant when he said I think therefore I am.
In his book the Problems of Philosophy, Bertrand Russell says this about the man who does not like philosophy
the man who has no tincture for philosophy goes through life imprisoned in the prejudices derived from common sense, from habitual beliefs of his age or his nation and from convictions which have grown up in his mind without the cooperation or consent of his deliberate reason.
He continues to say
to such a man, the world tends to become definite, finite, obvious; common objects raise no questions and unfamiliar possibilities are contemptuously rejected.
While admitting that philosophy is unable to provide us with some of the answers to the questions we seek, he has this to say
philosophy is able to suggest many possibilities which enlarge our thoughts and free them from tyranny of custom.
In this way
it greatly increases our knowledge as to what maybe; it removes the somewhat arrogant dogmatism of those who have never traveled into the region of liberating doubt and it keeps alive our sense of wonder by showing familiar things in an unfamiliar aspect.
In conclusion therefore,
philosophy is to be studied, not for the sake of any definite answers to its questions, since no definite answers can as a rule be known to be true but rather for the sake of the questions themselves, because these questions enlarge our conception of what is possible, enrich our intellectual imagination and diminish the dogmatic assurance which closes the mind against speculation; but above all because, through the greatness of the universe which philosophy contemplates, the mind also is rendered great and becomes capable of that union with the universe which constitutes its highest good.