"Remember the days of old, consider the years of many generations: ask thy father, and he shall shew thee; thy elders, and they shall tell thee." (Deuteronomy 32:7) "Remember ye not the former things, neither consider the things of old." (Isaiah 43:18)
The two verses sound like a contradiction, do they not? That's why a haphazard, cursory reading of the Word of God can sometimes bring more frustration than illumination. More often than not, it takes many readings to grasp its multi-faceted truths, and not many among us have the inclination to do it. This is unfortunate for many reasons, one being the sheer audacity of choosing to disregard the truest revelation we have of God now, and His message to us, His creation; another being that any seeming contradictions we see within its pages only come from our own inability to see all sides of a truth.
Having said that, let me point out what seems to me to be an obvious difference between the two texts which might help to account for their obviously dissimilar statements. Deuteronomy is talking about people (generations, fathers, elders); while Isaiah's argument is against preoccupation with things of the past. One deals with living history, and the other centers of dead tradition. With knowledge of history, we are offered insight into the successes and failures of those who have gone before, so that we might add their experiences into the mix our own decisions of conduct. Tradition, on the other hand, can only tell us what time it was, never what time it is, and carries with it the danger of stagnation. It can hold us back. If we're not careful, we may find ourselves acting by rote instead of reason.
By all means, learn history—written and oral. I am skeptical of anyone who is unwilling to look beyond his or her own experience. Familiarize yourself with God's dealings with men and women in the past, and learn from those who have seen His glory and lived their lives accordingly. The verse in Deuteronomy instructs us to do just that. But, at the same time, when God clearly opens His will to you, forget "the former things." Don't even consider
"the things of old." This is Isaiah's message to us.
At times (perhaps most of the time), God will expect us to walk as pilgrims; but there will undoubtedly come a time when He will ask us to walk as pioneers. At least, it may seem like that to those around us. It will be up to you and I, with the authority of the Word of God and under the tutelage of the Holy Spirit, to know the difference.
Know the past; live in the present; step boldly into the future.